Explanation:
The higher the charge of the ions, the stronger the electrostatic forces of attraction and, therefore, the greater the lattice enthalpy.
The smaller the ion, the greater the charge density and the stronger the electrostatic attraction between oppositely charged ions.
Statement I is incorrect since the smaller the lattice enthalpy, the weaker the electrostatic attraction and the lower the melting point is.

Explanation:
NH3 has all of the bonds/forces named above, but its high boiling point is due to the presence of hydrogen bonds which are the strongest intermolecular forces. Hydrogen bonding is possible due to the presence of N−H bonds.

Explanation:
Fluorine is the most electronegative element on the periodic table. Therefore, the greatest difference in electronegativity between $\mathrm{C}$ and $\mathrm{F}$ results in the most polar bond.

Explanation:
Triple bonds are stronger than double bonds which are in turn stronger than single bonds. The greater the number of shared pairs of electrons, the stronger the bond and the greater the bond enthalpy.

Explanation:
Neither material is electrically conductive. Diamond has no delocalized electrons, while the delocalized electrons in buckminsterfullerene are confined within the molecule. There is no extended lattice of bonds through which the electrons can move in response to an applied potential difference. Diamond is a hard material; a large force is required to break the strong covalent bonds between atoms.

Buckminsterfullerene, however, is soft, as only a small force is needed to overcome the weak intermolecular (London / dispersion) forces between molecules.

This question is moderately difficult, as the student must recall multiple features of the two carbon allotropes or deduce their physical properties from the diagrams given.

Explanation:
Oxidation reaction; Magnesium is much less electronegative than oxygen, so the Mg atoms lose electrons to the O atoms during the reaction. This process forms positive Mg2+ ions, termed cations, and negative O2− ions, termed anions.

This question is categorized as easy, as the student must recall two pieces of information that are covered extensively in the syllabus.

Explanation:
Volatility refers to the ease at which a substance vaporizes. Ionic bonds are very strong and, therefore, a lot of energy is required to turn ionic compounds into gases.

Polar solvents are able to form electrostatic forces of attraction with ions.

Explanation:
Non-metal elements bond to each other covalently. Ca3N2 is made up of a metal and a nonmetal (with a large difference in electronegativity) and has ionic bonding.

Explanation:
Recall that hydrogen bonds are the strongest intermolecular forces, and London forces are the weakest.

Explanation:
Choice A refers to ionic bonding;
Choice B could refer to ionic bonding or specifically coordinate (dative) bonding;
Choice C refers to hydrogen bonding.

Explanation:
Carboxylic acids have hydrogen bonding due to O−H bonds.

Explanation:
C3H6 belongs to the alkene class with the general formula CnH2n, and has a three carbon chain.

Explanation:
Oppositely charged ions attract, it is an ionic bonding;

Choice A describes metallic bonding;

Choice B describes a simple molecular lattice;

Choice D describes a covalent bond.

Explanation:
Electrostatic forces of attraction between the positive ions and delocalized electrons (metallic bonds) must be broken for metal to melt. The stronger the metallic bond, the higher the melting point.

Explanation:
Metals and non-metals have the greatest differences in electronegativity and so ionic bonds are formed.

Explanation:
There is no polyatomic ion with the formula of CO4 ^2−. The correct formula for the carbonate ion is CO3^2−. The formulas and charges of the other ions are correct.

Explanation:

Lithium is in group 1 and so forms Li+ ions. The formula of the nitride ion is N3−as nitrogen is in group 15. For the positive and negative charges to cancel out, three Li+ ions are needed for each N3− ion.

Explanation:
Metals characteristically have high melting points due to strong metallic bonds.

Explanation:
The strength of metallic bonding and therefore melting point, decreases down a group due to increasing atomic radius (more energy levels) and greater separation of the nuclei. Cs is in period 6, while all other 3 elements are in period 5. Hence, Cs has the lowest melting point. Since atomic radius decreases across a period due to increased effective nuclear charge, the strength of metallic bonding, and therefore melting point, increases from Rb to Zr.

Explanation:
SiO2 has a giant covalent structure where each Si atom is singly bonded to four oxygen atoms (while maintaining a Si

ratio of 1:2).
As there are four electron domains around each silicon atom, the structure has a tetrahedral arrangement. SiO2 is held together by strong covalent bonds requiring a large amount of energy to overcome, resulting in a high melting point.
The strong bonds, together with the fact that there are no charged particles present, lead to insolubility in polar solvents such as water.

Explanation:
There is no polyatomic ion with the formula of CO42−COX42−. The correct formula for the carbonate ion is CO32−COX32−. The formulas and charges of the other ions are correct.

Explanation:
Ionic bonds form between oppositely charged ions; NH4^+ and SO4^2− in ammonium sulfate and Na^+ and CO3^2− in sodium carbonate.

Due to a smaller difference in electronegativity and both being nonmetals, $\mathrm{l}$ bonds are polar covalent.

Explanation:
Non-metal elements bond to each other covalently. Ca3N2 is made up of a metal and a nonmetal (with a large difference in electronegativity) and has ionic bonding.

Explanation:
Simple molecular covalent structures cannot conduct electricity due to an absence of charged particles. $\mathrm{NaCl}$ is an ionic compound that has ions that are free to move when in a molten state.

Explanation:
The central atom is carbon with two C-H single bonds and one C=O bond. This gives 3 electron domains and 8 valence electrons.